General Licensing Class
G3A – G3C
Radio Wave Propagation
Your organization and dates here
General Class Element 3 Course Presentation
 ELEMENT 3 SUB-ELEMENTS
G1 – Commission’s Rules
G2 – Operating Procedures
G3 – Radio Wave Propagation
G4 – Amateur Radio Practices
G5 – Electrical Principles
G6 – Circuit Components
G7 – Practical Circuits
G8 – Signals and Emissions
G9 – Antennas
G0 – Electrical and RF Safety
2
Radio Wave Propagation
 The sunspot number is a measure of solar activity based on counting
sunspots and sunspot groups. (G3A01)
 The effect a Sudden Ionospheric Disturbance has on the daytime
ionospheric propagation of HF radio waves is that it disrupts signals
on lower frequencies more than those on higher frequencies. (G3A02)
A Sudden Ionic Disturbance
(SID) is a phenomenon that can
have a drastic effect on
propagation.
During an SID, the
sun emits a great
deal of ultraviolet
and X-ray radiation.
Radio Wave Propagation
 8 minutes is approximately how long it takes for the increased
ultraviolet and X-ray radiation from solar flares to affect radio-wave
propagation on the Earth. (G3A03)
 21 MHz and higher are the amateur radio HF frequencies that are least
reliable for long distance communications during periods of low solar
activity. (G3A04)
 The solar-flux index is a measure of solar radiation at 10.7 cm. (G3A05)
10.7 cm wavelength = 2.80 GHz
Radio Wave Propagation
 Geomagnetic activity, such as a geomagnetic storm, can also affect
radio propagation. A geomagnetic storm is a temporary disturbance
in the Earth's magnetosphere. (G3A06)
 At any point in the solar cycle, the 20 meter band usually supports
worldwide propagation during daylight hours. (G3A07)
 One of the effects a geomagnetic storm can have on radio-wave
propagation is degraded high-latitude HF propagation. (G3A08)
Radio Wave Propagation
• The effect that high sunspot numbers have on radio communications
is that long-distance communication in the upper HF and lower
VHF range is enhanced. (G3A09)
• The sunspot cycle is a long-term phenomenon. There are other
phenomena that affect radio wave propagation in the short term. For
example, the Sun’s rotation on its axis causes HF propagation
conditions to vary periodically in a 28-day cycle. (G3A10)
Solar flares and sunspots affect radiowave propagation
Radio Wave Propagation
• The phenomenon that most affects amateur radio communications on
the HF bands is the sunspot cycle. The typical sunspot cycle is
approximately 11 years long. (G3A11)
Notice 11 year cycles
2011 is coming into cycle 24.
Radio Wave Propagation
• There are two indices that give an indication of the stability of the
Earth’s magnetic field. The K-index indicates the short term stability
of the Earth’s magnetic field. (G3A12)
• The A-index indicates the long term stability of the Earth’s
geomagnetic field. (G3A13)
K Index
A Index
HF Skip Conditions
K1 - K4
A0 - A7
Bands are normal
K4
A8 - A15
Bands are unsettled
K4
A16 - A30
Bands are unpredictable
K5
A30 - A50
Lower bands are unstable
K6
A50 - A99
Few skywaves below 15 MHz
K7 - K9
A100 - A400
Radio blackout is likely
Go fishing or watch for an aurora.
Radio Wave Propagation
 HF communications are disturbed by the charged particles that
reach the Earth from solar coronal holes. (G3A14)
 It takes 20 to 40 hours for charged particles from Coronal Mass
Ejections (CME) to affect radio-wave propagation on the Earth. (G3A15)
A coronal mass ejection (CME) is a massive burst of solar wind and
magnetic fields rising above the solar corona or being released into space.
Coronal Mass Ejections take 20 – 40 hours to reach the earth where
ultraviolet and X-Ray radiation from solar flares take 8 minutes.
Radio Wave Propagation
• A possible benefit to radio communications resulting from periods of
high geomagnetic activity is that the aurora that can reflect VHF
signals. (G3A16)
Geomagnetic disturbances caused by the Sun result in the Northern Lights.
Radio Wave Propagation
•
While signals most often take the shortest path from point to point, sometimes
the best path for radio propagation is in the opposite direction, also called the
“long path.” A well-defined echo might be heard if a sky-wave signal arrives
at your receiver by both short path and long path propagation. (G3B01)
•
A good indicator of the possibility of sky-wave propagation on the 6 meter band
is that there is short skip sky-wave propagation on the 10 meter band. (G3B02)
•
When selecting a frequency for lowest attenuation when transmitting on HF,
select a frequency just below the MUF. (G3B03)
Radio Wave Propagation
• A reliable way to determine if the Maximum Usable Frequency (MUF) is
high enough to support skip propagation between your station and a
distant location on frequencies between 14 and 30 MHz is to listen for
signals from an international beacon. (G3B04)
There are websites that provide
skywave DX conditions.
Radio Wave Propagation
 When they are sent into the ionosphere, radio waves with
frequencies below the Maximum Usable Frequency (MUF) and
above the Lowest Usable Frequency (LUF) are bent back to the
Earth. (G3B05)
 When they are sent into the ionosphere, radio waves with
frequencies below the Lowest Usable Frequency (LUF) are
completely absorbed by the ionosphere. (G3B06)
 LUF stands for the Lowest Usable Frequency for communications
between two points. (G3B07)
 MUF stand for the Maximum Usable Frequency for
communications between two points. (G3B08)

Radio Wave Propagation
 2,500 miles is the approximate maximum distance along the Earth's
surface that is normally covered in one hop using the F2 region. (G3B09)
Radio Wave Propagation
 1,200 miles is the approximate maximum distance along the Earth's
surface that is normally covered in one hop using the E region. (G3B10)
 No HF radio frequency will support ordinary skywave communications
over the path when the Lowest Usable Frequency (LUF) exceeds the
Maximum Usable Frequency (MUF). (G3B11)
 The following factors affect the Maximum Usable Frequency (MUF) (G3B12)
• Path distance and location
• Time of day and season
• Solar radiation and ionospheric disturbances
All of these choices are correct.
Radio Wave Propagation
 The ionospheric layer closest to the surface of the Earth is the D layer.
(G3C01)
Altitudes in Miles of Ionospheric Layers
Day
 Where the Sun is overhead, ionospheric layers reach their maximum
height. (G3C02)
The ionosphere is what makes long-distance radio
communications possible on the shortwave bands.
The ionosphere is made up of three layers of charged
particles, labeled D, E, and F.
Radio Wave Propagation
• The F2 region is mainly responsible for the longest distance radio wave
propagation because it is the highest ionospheric region. (G3C03)
Radio Wave Propagation
Layers of the Atmosphere
Radio Wave Propagation
Atmospheric Layers
Terms we’ve heard before
from space shuttle launches.
Now apply them to Ham Radio
Ionosphere
31 – 400 miles
Stratosphere
6 – 31 miles
Troposphere
0 – 6 miles
Radio Wave Propagation
Regions in the Ionosphere
During the day....
 The “D” Region is closest to Earth
 The “D” Region absorbs MF/HF radio
signals
 The “F2” Region is most responsible
for long distance communication
At night....
 The “D” & “E” Regions disappear
 The “F1” & “F2” Regions combine into
one with reduced ionization
Radio Wave Propagation
• The highest takeoff angle that will return a radio wave to the
Earth under specific ionospheric conditions is called the critical
angle. (G3C04)
One factor that affects how well the ionosphere will reflect a
signal is the angle at which the signal impinges upon it.
If the angle is too high, it will pass right through the
ionosphere and not be reflected back to earth.
Radio Wave Propagation
 Long distance communication on the 40, 60, 80 and 160 meter bands
is more difficult during the day because the D layer absorbs signals
at these frequencies during daylight hours. (G3C05)
 When they are sent into the ionosphere, radio waves with
frequencies below the Lowest Usable Frequency (LUF) are
completely absorbed by the ionosphere. (G3B06)
 LUF stands for the Lowest Usable Frequency for communications
between two points. (G3B07)
 HF scatter signals in the skip zone are usually weak because only a
small part of the signal energy is scattered into the skip zone.
(G3C08)
Radio Wave Propagation
• One interesting propagation phenomenon is scatter propagation.
Scatter propagation allows a signal to be detected at a distance too far
for ground wave propagation but too near for normal sky-wave
propagation. (G3C09)
Scatter
Radio Wave Propagation
 An indication that signals heard on the HF bands are being received
via scatter propagation is that the signal is heard on a frequency
above the Maximum Usable Frequency. (G3C10)
 Horizontal dipoles placed between 1/8 and 1/4 wavelength above
the ground will be most effective for skip communications on 40
meters during the day. (G3C11)
•
Antennas used for DXing should have low takeoff angles.
•
One thing that affects the takeoff angle of an antenna is its height above ground.
Radio Wave Propagation
 The D layer is the ionospheric layer that is the most absorbent of
long skip signals during daylight hours on frequencies below 10
MHz. (G3C12)
F Layer
F Layer
E Layer
D Layer
E Layer
D Layer
Radio Wave Propagation
 Near Vertical Incidence Sky-wave (NVIS) propagation is short
distance HF propagation using high elevation angles. (G3C13)
The antenna sends the signal at an angle of close to 90 degrees,
and if conditions are right, the ionosphere reflects that signal back
to the earth at a very short distance from the transmitting station.